Detergent powders often contain minor amounts of coloured speckles or noodles which may be carriers for special additives such as catalysts, enzymes, fluorescers or photobleaches and/or may be used to highlight particular attributes of the detergent powders. The term "speckles" is used to denote granules or particles which are generally not too dissimilar to the granules or particles of the powder itself, other than in their colours, while the term "noodles" is used to refer to generally cylindrical particles prepared by extrusion and cutting or breaking: noodles generally, but not always, contain soap as a major ingredient. Coloured speckles have been used far more extensively than coloured noodles for two reasons: manufacture of satisfactory soap-based noodles can present problems, and the noodles themselves can be slow to dissolve when the detergent powder is used by the consumer.
Noodles based on soap are commonly produced by mixing dried soap chips with colourants and other minor ingredients, homogenising by working in either a mill or a refiner, and then extruding through a perforated plate with fine holes. They are generally extruded continuously and then allowed to weather sufficiently to break up into pieces from 3 to 15 mm in length. A series of rotating knives can be fitted to the face of the plate to cut the extruded noodles automatically into suitable lengths, but these tend to cause a certain amount of bunching to take place. The degree of bunching depends on the geometry of the cutting knives and holes, and is also greatly affected by the plasticity and stickiness of the noodles themselves. Even where a rotating knife is not used, the quality of the noodles is very dependent on the physical properties of the extruded soap. Ideally, the soap should be sufficiently plastic to extrude satisfactorily through the holes in the perforated plate but not so soft and sticky that they bunch together after extrusion. They should also be sufficiently hard and brittle to break up into the desired length range.
Another potential problem with soap-based noodles is their solubility and rate of dissolution. Although soap has excellent solubility in warm and hot water, the solubility in tepid water can be poor. Poor solubility of the soap noodles could therefore present a problem in a low sudsing detergent powder when used in automatic machines at low wash temperatures.
It has now been discovered that the manufacture of soap noodles is simplified and the dissolution improved, by incorporating in the noodles a certain proportion of free fatty acid and an inorganic salt.